1. some people used to think that a rocket could not travel to the moon because it would have no air to push aginst once it left the earths atmosphere. we now know that idea was mistaken. what force propels a rocket when it is in a vacuum?
2. since the force that acts on a bullet when a gun is fired is equal and opposite to the force that acts on the gun, does this imply a zero net force and therefore the impossibility of an accleration bullet?
3. suppose you exert 200N on your refrigerator and push it across the kitchen floor at constant velocity. what friction force acts between the refrigerator and the floor? is the friction force equal and opposite to ur 200N push? does the friction force make up the reaction force to your push?
2007-11-03 23:03:52 · 2 answers · asked by Anonymous in Science & Mathematics ➔ Physics
1.The rocket expell force at one end and that force is matched by a force going the opposite way.Jet engines work the same way.
2. Once the bullet leaves the gun,its speed decrease with air friction and it falls with gravity.
The only accelerating bullets are those shot from airplanes toward the ground.
3. Friction is dependent on what the refrigerator is being pushed on,if it is on wheels the coefficient of friction is minimal.
Different materials have different coefficients,tile floors cf.is much less than linoleum.
To move the refrigerator you got to overcame the weight (gravity)multiplied by the coefficient of friction (greek U).
2007-11-04 00:29:49 · answer #1 · answered by domedweller2 3 · 1⤊ 0⤋
you have it all wrong
air is merely the resistance, remove the air and things travel at the same speed for ever
rockets accelerate by reaction forces
the hot expanding gasses DO NOT PUSH AGAINST THE AIR , as they leave the nozzle they impart an opposite and equal reaction in the mass (that is the rocket)
2007-11-04 01:18:58 · answer #2 · answered by Anonymous · 0⤊ 1⤋